Generally, a construction machine such as a hydraulic excavator is constituted by an automotive lower traveling structure, an upper revolving structure which is swingably mounted on the lower traveling structure, and a working mechanism liftably mounted on the front side of the upper revolving structure. The upper revolving structure has an engine mounted on the rear side of a revolving frame to drive a hydraulic pump, and has a cab, a fuel tank, an operating oil tank, and the like mounted on the front side of the revolving frame.
Generally, a diesel engine is used as the engine of a hydraulic excavator. It is known that the diesel engine emits harmful substances such as particulate matter (PM) and nitrogen oxides (NOx), and the like. Accordingly, the hydraulic excavator is so constructed as to be provided with an exhaust gas treatment device in an exhaust pipe for forming an exhaust gas passage of the engine.
This exhaust gas treatment device has treatment members such as a particulate matter removing filter (which is generally called a diesel particulate filter and is hereinafter abbreviated as “DPF”) for capturing and removing the particulate matter in the exhaust gas, a selective reduction catalyst which purifies nitrogen oxides (NOx) by use of a urea water solution, and an oxidation catalyst for oxidizing and removing carbon monoxide (CO) and hydrocarbons (HC) (Patent Literature 1: Japanese Patent Laid-Open No. 2003-120277 A).
Here, the exhaust gas treatment device according to Patent Literature 1 is comprised of, for example, an upstream cylinder disposed on an upstream side in the flowing direction of exhaust gas of an engine, a downstream cylinder disposed on the downstream side, and a purifying part cylinder provided in series between these cylinders, and treatment members including DPF, a selective reduction catalyst, an oxidation catalyst, and the like, are accommodated in this purifying part cylinder. The upstream cylinder, the purifying part cylinder and the downstream cylinder have flanges at end portions opposing with each other, for example, and are connected in series in a state of sandwiching a gasket between the respective flanges for improving air-tightness therebetween.
Further, connecting portions opposing with each other are formed between the upstream cylinder and the purifying part cylinder and connecting portions opposing with each other are formed between the downstream cylinder and the purifying part cylinder. For example, the connecting portion of the upstream cylinder and the connecting portion of the downstream cylinder are formed of flanges, and each of the connecting portions opposing these flanges and disposed at both the ends of the purifying part cylinder respectively is formed of a flange and a projecting portion projecting from a position of the flange and inserted and fitted into the upstream cylinder and the downstream cylinder.
Incidentally, in the exhaust gas treatment device according to Patent Literature 1, the gasket is disposed to face the flange on the periphery of the projecting portion provided at each of both ends of the purifying part cylinder at the time of mounting and removing the purifying part cylinder to or from the upstream cylinder and the downstream cylinder. In this case, when the purifying part cylinder is inclined at the mounting and removing, the gasket slides down from the projecting portion downwardly inclined. Therefore, labors are required for the mounting and removing operation of the purifying part cylinder to or from the upstream cylinder and the downstream cylinder, raising a problem that an operational efficiency of an inspection operation, a cleaning operation or the like is degraded.